The question isn't entirely clear to me. What you can do is assist the
user in creating an XML file, essentially by continuously validating
whatever they type against the schema. Another possibility is to analyze the
schema, and then generate a minimal XML file that validates against it. The
XML Schema is *itself* an XML file, so you can "create" an XML document
simply by cloning the XML schema file itself, though there's no guarantee
this "resulting" document will validate against that Schema.

   - Oliver